Inkjet printing technology is used in many commercial products such as computer printers, graphics plotters, copiers, and facsimile machines. One type of inkjet printing, known as “drop on demand,” employs at least one inkjet pen that ejects drops of ink onto a print medium such as a sheet of paper. Printing fluids other than ink, such as preconditioners and fixers, can also be utilized. The pen or pens are typically mounted to a movable carriage that traverses back-and-forth across the print medium. As the pens are moved repeatedly across the print medium, they are activated under command of a controller to eject drops of printing fluid at appropriate times. With proper selection and timing of the drops, the desired pattern is obtained on the print medium.
An inkjet pen generally includes at least one fluid ejection device, commonly referred to as a printhead, which has a plurality of orifices or nozzles through which the drops of printing fluid are ejected. Adjacent to each nozzle is a firing chamber that contains the printing fluid to be ejected through the nozzle. Ejection of a fluid drop through a nozzle may be accomplished using any suitable ejection mechanism, such as thermal bubble or piezoelectric pressure wave. Capillary action causes the firing chamber to refill after drop ejection, drawing ink from the reservoir. An inkjet pen typically includes a pen supply line that delivers printing fluid from the printing fluid reservoir to the printhead.